Line scanning device for detecting defects in webs of material

Abstract

A line scanning device for detecting defects in webs of material, wherein a laser light source throws a light spot by way of an objective, a light deflector device, and a cylindrical lens onto a web of material moving parallel to its surface, the light spot periodically scanning the web at right angles to the direction of its movement and parallel to its surface, and wherein a light receiving arrangement comprising a rod light guide and at least one photoreceiver is disposed parallel to the web of material and to the direction of scanning. The rod light guide carries a step mirror arrangement on that side of its periphery lying opposite the light inlet, and a light-scattering cylindrical lens grid, the axes of whose lenses extend in the scanning direction, is disposed between the light source and the objective.

What is claimed is: 
     
       1. In a line scanning device for detecting defects in webs of material, wherein a laser light source throws a light spot by way of an objective, a light deflector device, and a cylindrical lens onto a web of material moving parallel to its surface, said light spot periodically scanning the web at right angles to the direction of its movement and parallel to its surface, and wherein a light receiving arrangement comprising a rod light guide having a first surface, a second surface opposite said first surface and having a longitudinal axis and at least one photoreceiver is disposed parallel to the web of material and to the direction of scanning; the improvement comprising a step mirror arrangement carried by said rod light guide along said first surface and parallel to said axis, on that side of its periphery lying opposite the light inlet to said guide, and comprising a plurality of mirrors inclined with respect to said longitudinal axis, and arranged substantially exactly one behind the other when looking in the direction of said axis such that light reflected by said mirrors impinges on said second surface at angles of total reflection, and a light-scattering cylindrical lens grid, the axes of whose lenses extend in the scanning direction, disposed between the light source and said objective. 
     
     
       2. A device according to claim 1, wherein the cylindrical lens grid is situated at the focal point of the objective. 
     
     
       3. A device according to claim 1, wherein the cylindrical lens grid is axially displaced slightly from the focal point of the objective. 
     
     
       4. A device according to claim 3, wherein the distance from the focal point amounts to from 5 to 20 percent, of the focal length of the objective. 
     
     
       5. A device according to claim 1, wherein the cylindrical lens grid is displaceable in the direction of the optical axis. 
     
     
       6. A device according to claim 1, wherein the cross-section of the light beam falling on the cylindrical lens grid covers at least five juxtaposed negative lenses of the cylindrical lens grid. 
     
     
       7. A device according to claim 1, wherein the rod light guide is circular. 
     
     
       8. A device according to claim 1, wherein the diameter of the rod light guide is at least five times as great as the width of the step mirror arrangement. 
     
     
       9. A device according to claim 8, wherein said diameter is about twenty times said width. 
     
     
       10. A device according to claim 1, wherein the light beam passes through a beam widening optical system before it impinges on the objective. 
     
     
       11. A device according to claim 10, wherein the widening optical system comprises first and second crossed cylindrical lenses. 
     
     
       12. A device according to claim 11, wherein the axis of the first cylindrical lens extends at right angles to the axis of the mirror wheel. 
     
     
       13. A device according to claim 11, wherein the focal length of the first and second cylindrical lenses are in the ratio of approximately 10:1. 
     
     
       14. A device according to claim 11, wherein the focal line of the second cylindrical lens coincides with the focal point of the objective. 
     
     
       15. A device according to claim 1, wherein a light-scattering cylindrical lens grid comprising negative cylindrical lenses extending at right angles to the axis of the rod light guide is provided between the web of material and the light receiving arrangement. 
     
     
       16. A device according to claim 11, wherein the first cylindrical lens is adapted to be displaceable in the axial direction or exchangeable. 
     
     
       17. A device according to claim 1, wherein between the web of material and the rod light guide a cylindrical lens is disposed which concentrates the light on the step mirror arrangement. 
     
     
       18. A device according to claim 1, wherein the light inlet of an Ulbricht sphere, at whose light outlet the photoreceiver is disposed, is provided at at least one end face of the rod light guide. 
     
     
       19. A device according to claim 18 wherein the direct light path from the light inlet to the light outlet of the Ulbricht sphere is interrupted by a diaphragm. 
     
     
       20. A device according to claim 18, wherein at the other end of the rod light guide an Ulbricht sphere is likewise provided. 
     
     
       21. A device according to claim 18, wherein the light inlet and light outlet openings of the Ulbricht sphere are at right angles to one another. 
     
     
       22. A device according to claim 16, wherein at the other end of the rod light guide a mirror coating is provided.